成员变量的初始化与构造函数

#include <iostream>
using namespace std;
class demo {
public:
	demo() {
		x = 0;
		cout << "demo的默认构造函数!" << x << endl;
	}
	demo(int i) {//此构造方法被调用两次
		x = i;
		cout << "demo的带一个参数的构造函数!" << x << endl;
	}
	~demo() {//析构方法在最后调用两次
		cout << "demo的默认析构函数!" << x << endl;
	}
	int get() {
		return x;
	}
	void set(int i) {
		x = i;
	}
private:
	int x;
};
class rectangle {
public:
	rectangle() {
		x = 1000;
		cout << "rectangle的默认构造函数!" << x << endl;
	}
	rectangle(int i, int j, int k) :
		x(i), width(j), length(k) {//调用过程按照成员变量的先后顺序
		cout << "rectangle的带三个参数的构造函数!" << "长方形b的面积为:" << length.get()
				* width.get() << endl;
	}
	~rectangle() {
		cout << "rectangle的默认析构函数!" << x << endl;
	}
	int area() {
		return length.get() * width.get();
	}
private:
	demo length;//成员变量列表包含其他类对象叫做包容
	demo width;
	int x;
};
int main() {
	rectangle a(100,200,300);
	return 0;
}